The present invention relates to a coating type high capacity magnetic recording medium (i.e., a high capacity magnetic recording particulate medium).
Magnetic heads working with electromagnetic induction as the principle of operation (an induction type magnetic head) are conventionally used and spread. However, magnetic heads of this type are approaching their limit for use in the field of higher density recording and reproduction. That is, it is necessary to increase the number of winding of the coil of a reproduction head to obtain larger reproduction output, but when the winding number is increased, the inductance increases and the resistance at high frequency heightens, as a result, the reproduction output lowers.
In recent years, reproduction heads which work with MR (magneto-resistance) as the principle of operation are proposed and come to be used in hard discs. As compared with the induction type magnetic head, several times of reproduction output can be obtained by the MR head. Further, since an induction coil is not used in the MR head, noises generated from instruments, e.g., impedance noises, are largely reduced, therefore, it becomes possible to obtain a great S/N ratio by lowering the noise coming from magnetic recording media. In other words, good recording and reproduction can be done and high density recording characteristics can be drastically improved by lessening the noise of magnetic recording media hiding behind the instruments.
It is known that a magnetic recording medium using a barium ferrite (hereinafter referred to as xe2x80x9cBa ferritexe2x80x9d) magnetic powder is excellent in the stability of magnetic characteristics resulting from the chemical stability of a magnetic powder as compared with a magnetic recording medium using a metallic magnetic powder. On the other hand, a high capacity magnetic recording medium shows a tendency to use a Ba ferrite of finer particles to reduce noises.
When a magnetic recording medium using a fine particle Ba ferrite powder is stored under a high temperature and high humidity condition, drawbacks arise in the stability of recording and reproduction, such as the reduction of output, the dropout and the clogging of a head.
An object of the present invention is to provide a magnetic recording medium which is free of head clogging, not accompanied with the reduction of output, less in the dropout and excellent in the stability of recording and reproduction even when the magnetic recording medium is stored under a high temperature and high humidity condition.
The present invention has been achieved by a magnetic recording medium comprising a support having provided thereon a magnetic layer containing a barium ferrite powder dispersed in a binder, wherein the concentration of Ba of the extract obtained by the following condition is 20 ppm or less per m2 of the magnetic recording medium:
condition: 0.05 m2 of the magnetic recording medium is arbitrarily cut out and put in a 200 ml beaker with 100 ml of distilled water, the beaker is covered with a watch glass and retained in a constant temperature bath at 75xc2x0 C. for 3 hours.
A preferred mode of the present invention is as follows.
(1) The magnetic recording medium, wherein the specific surface area of the barium ferrite powder is 40 m2/g or higher.